U.S. Pat. No. 4,929,517, granted May 29, 1990 to W. L. Luoma, et al., discloses a typical acid electrolyte fuel cell assembly of the type used to build multi-cell fuel cell stacks for commercial production of electricity from natural gas and air reactants. Each cell assembly will include an electrolyte matrix which is a porous plate saturated with electrolyte. The electrolyte matrix will be sandwiched between anode and cathode electrode substrates, which are porous plates on which reaction-enabling catalyst layers are deposited in which the fuel cell reaction takes place. Outwardly of the electrode substrates are anode and cathode reactant flow field plates which are porous carbon bodies that have reactant flow channels formed in them which face the electrode substrates. The reformed fuel and oxidant thus flow through their respective flow field channels and diffuse through the electrode substrates toward the electrolyte matrix. The anode and cathode flow field plates are carbon-carbon composites, i.e., they are composed of carbon powder particles which are bonded together by a polymer binder that is converted to carbon and further heat treat at temperatures sufficient to graphitize the material. These plates are both hydrophilic, and both serve as electrolyte reservoir plates (ERPs) in which excess electrolyte can be stored in a manner that will allow the electrolyte to diffuse from the ERPs into the electrolyte matrix and edge seals, as needed. The adjacent cell assembly in a fuel cell stack will be separated by an electrically conductive separator plate that will conduct electrons, but will block migration of electrolyte and reactants between adjacent cell assemblies. The separator plates will be bonded to the cathode flow field plates of one cell, and to the anode flow field plates of the adjacent cell by fluorocarbon films, which are useful in binding the entire stack assembly together, and which tend to block electrolyte migration between adjacent cell assemblies. The ERPs also will be provided with some sort of edge seals to prevent reactant leakage from the cathode side to the anode side or vice versa of the cells during stack operation. These seals are typically wet or dry seals. Wet seals rely on very small pore sizes at the edges of the EPRs, which are filled with other electrolyte so that the reactant flow will be resisted. Dry seals are typically formed from mixtures of hydrophobic binders such as polytetrafluoroethylene (PTFE) or the like and a compatible filler such as graphite.
A problem attendant to the use of carbon/fluorocarbon plates relates to the relatively large amount of the fluorocarbon resin binder needed to form the plates when spheroidal carbon particles are used. The fluorocarbon resins have a high coefficient of thermal expansion whereby the prior art plates have a low thermal expansion coefficient. The difference in coefficients of thermal expansion creates stresses between components which can lead to cracks and component failure. The thermal expansion and contraction of the plates will cause stack component discontinuities which can lead to cell damage; and will cause flow field plate cracking which also leads to cell failure.
Still another drawback with the carbon/carbon reactant flow field plates is the requirement that they be heat treated at temperatures in the range of 2,500.degree. to 3,000.degree. C. in order to convert the carbon polymer to carbon, and to create the desired physical properties needed to function as an electrolyte reservoir plate. This significantly increases the cost of this component.